The present invention relates to a liquid crystal display device of the type used for a personal computer or a work station, particularly, the invention relates to a technique to be effectively applied to a video signal line driving circuit (drain driver) of a liquid crystal display for the purpose enabling multilevel gradation display.
An active-matrix liquid crystal display made up of an active element (e.g., thin film transistor) for each pixel and operating to produce a display by switching the active element is widely used as a display for a notebook computer. Because, in the active-matrix liquid crystal display, a video signal voltage (gradation voltage) is applied to a pixel electrode through an active element, there is no crosstalk between pixels, and so it is unnecessary to use a special driving method for preventing crosstalk, unlike a passive-matrix liquid crystal display. Thus, with an active-matrix liquid crystal display, multilevel gradation display is possible.
A TFT liquid crystal display module, provided with a TFT (Thin Film Transistor) liquid crystal display panel (TFT-LCD), a drain driver provided on the upper side of the liquid crystal display panel, and a gate driver and an interface section provided on the side of the liquid crystal display panel, is a known type of active-matrix liquid crystal display.
The TFT liquid crystal display module has a multilevel gradation voltage generation circuit in the drain driver and, moreover, has a gradation voltage selection circuit for selecting a gradation voltage corresponding to display data, out of multilevel gradation voltages generated by the multilevel gradation voltage generation circuit in order to realize multilevel gradation display. This technique is disclosed in Japanese Patent Application No. 8-86668 published as Japanese Unexamined Patent Application Publication No. 8-281930.
In general, the gradation voltage selection circuit in the drain driver has a transistor group for selecting gradation voltages of multilevel gradation generated by the multilevel gradation voltage generation circuit in the drain driver, whose gate electrode is provided with a transistor group to whose electrodes the bit values of display data are applied.
For example, the gradation voltage generation circuit generates gradation voltages of 64 levels. Moreover, when it is assumed that the gradation voltage generation circuit is a decoder circuit to which bit values and their inverted bit values of 6-bit display data are input, 12 transistors are cascade-connected to the gradation voltage selection circuit for each of 64 levels of gradation.
Meanwhile, in the case of a liquid crystal display, multilevel gradation display has further progressed from a 64-level gradation display to a 256-level gradation display in recent years.
Moreover, to display a picture having such a multilevel gradation on a liquid crystal display panel, the gradation voltage selection circuit in the drain drive requires 16 transistors for each of 256 levels of gradation. Therefore, there are problems is that the area occupied by the gradation voltage selection circuit increases in size, and the chip size of the semiconductor integrated circuit (IC chip) constituting the drain driver increases.
Furthermore, in the case of a liquid crystal display, such as a TFT liquid crystal display module, the display screen is further increased in scale, and, therefore, the display screen size tends to be increased. Furthermore, to eliminate unnecessary spaces and improve the fine appearance of the display, it is necessary to minimize those regions outside the display region of the display, that is, minimize the frame portion of the display (frame minimization).
However, when the area occupied by the gradation voltage selection circuit increases and the chip size of the semiconductor integrated circuit (IC chip) constituting the drain driver increases, there arises a problem in that these increases directly conflict with the need for frame minimization.
The present invention has been made to solve the above-mentioned problems, and its object is to provide a technique for making it possible for a liquid crystal display to generate gradation voltages having more gradations, such as 256 gradations, without increasing the chip size of the video signal line driving circuits.
The above object and novel features of the present invention will become apparent from the description provided by this specification and the accompanying drawings.
An outline of typical features of the invention disclosed in this application will be briefly described below.
A liquid crystal display is provided with a liquid crystal panel having a plurality of pixels and a driving circuit for applying a video signal voltage to each of the pixels in accordance with display data, wherein
the driving circuit has a first circuit for outputting is two voltages in accordance with one display data value and a second circuit for outputting one of a plurality of voltages generated from the two voltages.
The liquid crystal display is provided with a liquid crystal panel having a plurality of pixels arranged like a matrix and a driving circuit for applying a video signal voltage to each of the pixels in accordance with display data, wherein
the driving circuit has a first circuit for outputting a first voltage and a second voltage in accordance with one display data value, a second circuit for receiving the first and second voltages and outputting one of a plurality of voltages generated from the first and second voltages, and a switch circuit for switching input terminals of the second circuit to which the first and second voltages are input.
The liquid crystal display is provided with a liquid crystal panel having a plurality of pixels arranged like a matrix and a driving circuit for applying a video signal voltage to each of the pixels in accordance with display data, wherein
the driving circuit has a first circuit for outputting a first voltage and a second voltage in accordance with first display data, and for outputting the first voltage and a third voltage in accordance with second display data, and a second circuit for receiving two voltages output by the first circuit and for outputting one of a plurality of voltages generated from two voltages output by the first circuit.
The liquid crystal display is provided with a liquid crystal panel having a plurality of pixels arranged like a matrix and a driving circuit for applying a video signal voltage to each of the pixels in accordance with m-bit display data, wherein
the driving circuit has a first voltage generation circuit for generating (2n+1) (where 2xe2x89xa6nxe2x89xa6m) first gradation voltages and
a second voltage generation circuit for receiving two voltages output by the first voltage generation circuit in accordance with high-order n-bit data of the m-bit display data, and for outputting one of a plurality of voltages generated from two voltages outputted by the first voltage generation circuit in accordance with low-order (mxe2x88x92n)-bit data of the m-bit display data.
The liquid crystal display is provided with a liquid crystal panel having a plurality of pixels arranged like a matrix and a driving circuit for applying a video signal voltage to each of the pixels in accordance with m-bit display data, wherein
the driving circuit has a first voltage generation circuit for generating (2n+1) (where 2xe2x89xa6nxe2x89xa6m) first gradation voltages and for outputting two voltages in accordance with high-order e-bit data of the m-bit display data, a second voltage generation circuit for receiving two voltages outputted by the first voltage generation circuit at a first input terminal and a second input terminal and for outputting one of a plurality of voltages generated from two voltages outputted by the first voltage generation circuit in accordance with low-order (mxe2x88x92n)-bit data of the m-bit display data, and a switch circuit for connecting the output of the first voltage generation circuit to the first and second input terminals.